Fuel leak detection in fuel cell stack

ABSTRACT

The present disclosure generally relates to systems and methods for detecting a hydrogen leak in a fuel cell system including initiating a shutdown process of a fuel cell stack in the fuel cell system by a controller, measuring a volume of hydrogen in a reservoir, pulsing a volume of hydrogen into the reservoir or pulsing hydrogen directly into the fuel cell stack if the volume of hydrogen is insufficient to sustain a voltage discharge process during the shutdown process, making the fuel cell system enter a discharge state by the controller, wherein hydrogen and oxygen in the fuel cell stack are consumed in an electrochemical reaction to discharge voltage in the fuel cell stack, measuring a rate of the voltage discharge by the controller, and detecting the hydrogen leak based on the rate of the voltage discharge or via negative pressure measurements made at the anode inlet.

CROSS-REFERENCE TO RELATED APPLICATIONS

This nonprovisional application claims the benefit and priority, under35 U.S.C. § 119(e) and any other applicable laws or statutes, to U.S.Provisional Patent Application Ser. No. 63/313,832 filed on Feb. 25,2022, the entire disclosure of which is hereby expressly incorporatedherein by reference.

TECHNICAL FIELD

The present disclosure relates to systems and methods for detecting afuel leak in a fuel cell system.

BACKGROUND

The fuel cell is a multi-component comprising a membrane electrodeassembly (MEA) at the center, a gas diffusion layer (GDL) on both sidesof the membrane electrode assembly (MEA), and a bipolar plate (BPP) onthe other side of the gas diffusion layer (GDL). The membrane electrodeassembly (MEA) is a component that enables electrochemical reactions inthe fuel cell. The GDL positioned adjacent to the MEA facilitates thediffusion of reactants, manages the water transport within the fuel cellstack, protects the MEA from the flow field channels, and improveselectrical conductivity.

During fuel cell stack shutdown, reactants may still be present at theanode (e.g., hydrogen or a hydrocarbon) and the cathode (e.g., air). Thereactants can travel through the micropores of a membrane in the MEA.However, the membrane may develop a gas crossover leak due to age,usage, and/or environment contamination, Additionally, or alternativelyan external leak may develop due to poor sealing or faulty bipolarplates.

Detection of such leaks is essential for optimizing operation of thefuel cell system. Hydrogen leaks within fuel cell systems may cause harmor affect the efficacy of the system. Hydrogen is a flammable gas thatwhen released in confined spaces, non-ventilated, or poorly ventilatedareas may lead to a fire and/or an explosion. Thus, the presentdisclosure is directed to systems and methods to detect hydrogen leaksbased on the voltage discharged in the fuel cell system or based on thechange in pressure at the anode of the fuel cell system.

SUMMARY

Embodiments of the present disclosure are included to meet these andother needs.

A one aspect, described herein, is a method of detecting a hydrogen leakin a fuel cell system. The method comprises initiating a shutdownprocess of a fuel cell stack in the fuel cell system by a controller,measuring a volume of hydrogen in a hydrogen reservoir, replenishing thevolume of hydrogen in the reservoir when the volume of hydrogen cannotsustain a voltage discharge during the shutdown process, dischargingvoltage in the fuel cell stack of the fuel cell system by thecontroller, wherein hydrogen and oxygen in the fuel cell stack areconsumed in an electrochemical reaction, measuring a rate of the voltagedischarge by the controller, and detecting the hydrogen leak based onthe rate of the voltage discharge.

In some embodiments, the system may comprise detecting an open purgevalve in the fuel cell system. In some embodiments, the voltage may bedischarged by a discharge resistor. In some embodiments, the hydrogenleak may occur through an external leak or through an anode to cathodecrossover in the fuel cell stack.

In some embodiments, the method may comprise detecting the hydrogen leakbased on the rate of the voltage discharge comprises correlating therate of voltage discharge to an expectant rate of voltage discharge inthe fuel cell stack. In some embodiments, the method may comprisecorrelating the rate of voltage discharge to the expectant rate ofvoltage discharge comprises utilizing a look-up table, a map, anexperimental data, or a calculation.

In some embodiments, the method may comprise monitoring a minimum anodenegative pressure achieved in a predetermined time period. In someembodiments, the method may comprise determining that a hydrogen supplyvalve and one or more purge valves in the fuel cell system are closedbefore monitoring the minimum anode negative pressure. In someembodiments, the method may comprise correlating the minimum anodenegative pressure to an acceptable leak value based on a baseline levelof an acceptable leak for the fuel cell stack at beginning of life ofthe fuel cell stack.

In some embodiments, the method may comprise monitoring a minimum anodenegative pressure achieved for an additional period after has the fuelcell stack has been discharged to a stack voltage of about 5V.

In another aspect, described herein, is a fuel cell system. The fuelcell system may comprise a fuel cell stack including an anode and acathode, a discharge resistor operable to discharge voltage from thefuel cell stack, a system controller operable to measure a rate ofvoltage discharge, and determine or identify a presence of a hydrogenleak in the fuel cell system based on the discharge voltage.

In some embodiments, the system controller may be operable to determinethe hydrogen leak based on a measurement of a minimum anode negativepressure achieved in a predetermined time period. In some embodiments,the additional time period may range from about 2 minutes to about 2hours. In some embodiments, the system controller may use a look-uptable, a map, an experimental data, or a calculation to determine thehydrogen leak. In some embodiments, the system controller may beoperable to identify the presence of the hydrogen leak based on a rateof pressure drop in the anode or a hydrogen manifold at the end ofoperation of the fuel cell system.

In some embodiments, the pressure drop is after an additional timeperiod after the end of operation of the fuel cell system. In someembodiments, the additional time period may be about 1 second to about300 seconds.

In some embodiments, the system controller may be operable to identifythe hydrogen leak of greater than about 200 μm in diameter. In someembodiments, the discharge resistor may be operable to discharge voltagefrom the fuel cell stack for voltage discharge time, and wherein thecontroller may be operable to output an error message indicating thatthe hydrogen leak check has failed if the voltage discharge time is lessthan a predetermined discharge time period. In some embodiments, thepredetermined discharge time period may be about 1 second to about 50seconds.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects, and advantages of the presentinvention will become better understood when the following detaileddescription is read with reference to the accompanying drawings, inwhich like characters represent like parts throughout the drawings,wherein:

FIG. 1A is a schematic view of an exemplary fuel cell system includingan air delivery system, a hydrogen delivery system, and a fuel cellmodule including a stack of multiple fuel cells;

FIG. 1B is a cutaway view of an exemplary fuel cell system including anair delivery system, hydrogen delivery systems, and a plurality of fuelcell modules each including multiple fuel cell stacks;

FIG. 1C is a perspective view of an exemplary repeating unit of a fuelcell stack of the fuel cell system of FIG. 1A;

FIG. 1D is a cross-sectional view of an exemplary repeating unit of thefuel cell stack of FIG. 1C;

FIG. 2 is a schematic of an example of one embodiment of a fuel cellstack system;

FIG. 3 is an illustration of a method of leak detection based on therate of voltage discharge from a fuel cell stack;

FIG. 4 is an illustration of a method of leak detection based on theminimum anode inlet stack pressure in a fuel cell stack;

FIG. 5 is an illustration of a method of leak detection based on thebased on the decay rate of anode stack inlet pressure in a fuel cellstack; and

FIG. 6 is an illustration of a method of leak detection based on thebased on the decay rate of decay rate of hydrogen manifold pressure.

DETAILED DESCRIPTION

The present disclosure relates to systems and methods for detecting fuelleak in a fuel cell system. The present disclosure is directed toimplementing a controller to determine, predict, or identify a hydrogenleak in a fuel cell system based on a rate of stack voltage discharge inthe fuel cell system or on the basis of a minimum anode stack inletpressure in the fuel cell system. The present disclosure is directed tohydrogen leaks that may occur at multiple different locations in thefuel cell system.

As shown in FIG. 1A, fuel cell systems 10 often include one or more fuelcell stacks 12 or fuel cell modules 14 connected to a balance of plant(BOP) 16, including various components, to support the electrochemicalconversion, generation, and/or distribution of electrical power to helpmeet modern day industrial and commercial needs in an environmentallyfriendly way. As shown in FIGS. 1B and 1C, fuel cell systems 10 mayinclude fuel cell stacks 12 comprising a plurality of individual fuelcells 20. Each fuel cell stack 12 may house a plurality of fuel cells 20assembled together in series and/or in parallel. The fuel cell system 10may include one or more fuel cell modules 14 as shown in FIGS. 1A and1B.

Each fuel cell module 14 may include a plurality of fuel cell stacks 12and/or a plurality of fuel cells 20. The fuel cell module 14 may alsoinclude a suitable combination of associated structural elements,mechanical systems, hardware, firmware, and/or software that is employedto support the function and operation of the fuel cell module 14. Suchitems include, without limitation, piping, sensors, regulators, currentcollectors, seals, and insulators.

The fuel cells 20 in the fuel cell stacks 12 may be stacked together tomultiply and increase the voltage output of a single fuel cell stack 12.The number of fuel cell stacks 12 in a fuel cell system 10 can varydepending on the amount of power required to operate the fuel cellsystem 10 and meet the power need of any load. The number of fuel cells20 in a fuel cell stack 12 can vary depending on the amount of powerrequired to operate the fuel cell system 10 including the fuel cellstacks 12.

The number of fuel cells 20 in each fuel cell stack 12 or fuel cellsystem 10 can be any number. For example, the number of fuel cells 20 ineach fuel cell stack 12 may range from about 100 fuel cells to about1000 fuel cells, including any specific number or range of number offuel cells 20 comprised therein (e.g., about 200 to about 800). In anembodiment, the fuel cell system 10 may include about 20 to about 1000fuel cells stacks 12, including any specific number or range of numberof fuel cell stacks 12 comprised therein (e.g., about 200 to about 800).The fuel cells 20 in the fuel cell stacks 12 within the fuel cell module14 may be oriented in any direction to optimize the operationalefficiency and functionality of the fuel cell system 10.

The fuel cells 20 in the fuel cell stacks 12 may be any type of fuelcell 20. The fuel cell 20 may be a polymer electrolyte membrane orproton exchange membrane (PEM) fuel cell, an anion exchange membranefuel cell (AEMFC), an alkaline fuel cell (AFC), a molten carbonate fuelcell (MCFC), a direct methanol fuel cell (DMFC), a regenerative fuelcell (RFC), a phosphoric acid fuel cell (PAFC), or a solid oxide fuelcell (SOFC). In an exemplary embodiment, the fuel cells 20 may be apolymer electrolyte membrane or proton exchange membrane (PEM) fuel cellor a solid oxide fuel cell (SOFC).

In an embodiment shown in FIG. 1C, the fuel cell stack 12 includes aplurality of proton exchange membrane (PEM) fuel cells 20. Each fuelcell 20 includes a single membrane electrode assembly (MEA) 22 and a gasdiffusion layers (GDL) 24, 26 on either or both sides of the membraneelectrode assembly (MEA) 22 (see FIG. 1C). The fuel cell 20 furtherincludes a bipolar plate (BPP) 28, 30 on the external side of each gasdiffusion layers (GDL) 24, 26, as shown in FIG. 1C. The above-mentionedcomponents, in particular the bipolar plate 30, the gas diffusion layer(GDL) 26, the membrane electrode assembly (MEA) 22, and the gasdiffusion layer (GDL) 24 comprise a single repeating unit 50.

The bipolar plates (BPP) 28, 30 are responsible for the transport ofreactants, such as fuel 32 (e.g., hydrogen) or oxidant 34 (e.g., oxygen,air), and cooling fluid 36 (e.g., coolant and/or water) in a fuel cell20. The bipolar plates (BPP) 28, 30 can uniformly distribute reactants32, 34 to an active area 40 of each fuel cell 20 through oxidant flowfields 42 and/or fuel flow fields 44 formed on outer surfaces of thebipolar plates (BPP) 28, 30. The active area 40, where theelectrochemical reactions occur to generate electrical power produced bythe fuel cell 20, is centered, when viewing the stack 12 from a top-downperspective, within the membrane electrode assembly (MEA) 22, the gasdiffusion layers (GDL) 24, 26, and the bipolar plate (BPP) 28, 30.

The bipolar plates (BPP) 28, 30 may each be formed to have reactant flowfields 42, 44 formed on opposing outer surfaces of the bipolar plate(BPP) 28, 30, and formed to have coolant flow fields 52 located withinthe bipolar plate (BPP) 28, 30, as shown in FIG. 1D. For example, thebipolar plate (BPP) 28, 30 can include fuel flow fields 44 for transferof fuel 32 on one side of the plate 28, 30 for interaction with the gasdiffusion layer (GDL) 26, and oxidant flow fields 42 for transfer ofoxidant 34 on the second, opposite side of the plate 28, 30 forinteraction with the gas diffusion layer (GDL) 24. As shown in FIG. 1D,the bipolar plates (BPP) 28, 30 can further include coolant flow fields52 formed within the plate (BPP) 28, 30, generally centrally between theopposing outer surfaces of the plate (BPP) 28, 30. The coolant flowfields 52 facilitate the flow of cooling fluid 36 through the bipolarplate (BPP) 28, 30 in order to regulate the temperature of the plate(BPP) 28, 30 materials and the reactants. The bipolar plates (BPP) 28,30 are compressed against adjacent gas diffusion layers (GDL) 24, 26 toisolate and/or seal one or more reactants 32, 34 within their respectivepathways 44, 42 to maintain electrical conductivity, which is requiredfor robust operation of the fuel cell 20 (see FIGS. 1C and 1D).

The fuel cell system 10 described herein, may be used in stationaryand/or immovable power system, such as industrial applications and powergeneration plants. The fuel cell system 10 may also be implemented inconjunction with an air delivery system 18. Additionally, the fuel cellsystem 10 may also be implemented in conjunction with a hydrogendelivery system and/or a source of hydrogen 19 such as a pressurizedtank, including a gaseous pressurized tank, cryogenic liquid storagetank, chemical storage, physical storage, stationary storage, anelectrolysis system or an electrolyzer. In one embodiment, the fuel cellsystem 10 is connected and/or attached in series or parallel to ahydrogen delivery system and/or a source of hydrogen 19, such as one ormore hydrogen delivery systems and/or sources of hydrogen 19 in the BOP16 (see FIG. 1A). In another embodiment, the fuel cell system 10 is notconnected and/or attached in series or parallel to a hydrogen deliverysystem and/or a source of hydrogen 19.

The present fuel cell system 10 may also be comprised in mobileapplications. In an exemplary embodiment, the fuel cell system 10 is ina vehicle and/or a powertrain 100. A vehicle 100 comprising the presentfuel cell system 10 may be an automobile, a pass car, a bus, a truck, atrain, a locomotive, an aircraft, a light duty vehicle, a medium dutyvehicle, or a heavy-duty vehicle. Type of vehicles 100 can also include,but are not limited to commercial vehicles and engines, trains,trolleys, trams, planes, buses, ships, boats, and other known vehicles,as well as other machinery and/or manufacturing devices, equipment,installations, among others.

The vehicle and/or a powertrain 100 may be used on roadways, highways,railways, airways, and/or waterways. The vehicle 100 may be used inapplications including but not limited to off highway transit, bobtails,and/or mining equipment. For example, an exemplary embodiment of miningequipment vehicle 100 is a mining truck or a mine haul truck.

In addition, it may be appreciated by a person of ordinary skill in theart that the fuel cell system 10, fuel cell stack 12, and/or fuel cell20 described in the present disclosure may be substituted for anyelectrochemical system, such as an electrolysis system (e.g., anelectrolyzer), an electrolyzer stack, and/or an electrolyzer cell (EC),respectively. As such, in some embodiments, the features and aspectsdescribed and taught in the present disclosure regarding the fuel cellsystem 10, stack 12, or cell 20 also relate to an electrolyzer, anelectrolyzer stack, and/or an electrolyzer cell (EC). In furtherembodiments, the features and aspects described or taught in the presentdisclosure do not relate, and are therefore distinguishable from, thoseof an electrolyzer, an electrolyzer stack, and/or an electrolyzer cell(EC).

Referring back to a fuel cell system 10, stack 12, or cell 20, a gas(e.g., hydrogen) may crossover from an anode to a cathode side or fromthe cathode to the anode side during operation or shutdown to create aleak. This leak (also referred to as a gas crossover, a crossover leakor crossover leakage, a hydrogen leak, or a hydrogen crossover leak) inthe fuel system 10, stack 12, or cell 20 may occur because of existingconcentration gradients, pressure gradients, and/or permeability of theMEA 22. This hydrogen crossover leak across the MEA 22 may develop overtime due to usage of and/or age of the fuel cell stack 12.

Additionally, hydrogen supply pressure may also result in a differentminimum negative pressure at the anode inlet 114. The system or methodof the present disclosure also accounts for the crossover leak as itrelates to varying hydrogen supply pressure. When hydrogen is lost, andnot electrochemically consumed due to the crossover leak, fuel cell 20,stack 12, and system 10 efficiency may decrease and electrode (e.g.,anode and/or cathode) degradation may occur.

Direct combustion of hydrogen and/or oxygen create heat that may resultin the degradation of the MEA 22, resulting in the formation of apinhole in the MEA 22. Alternatively or additionally, particulates fromthe fuel or oxidant may enter the fuel cell stack 12 and result in apinhole in the MEA 22 of the fuel cell stack 12.

While typically ranging from about 1/10000 inch to about 1/10 inch indiameter when formed, with usage of the fuel cell stack 12, the pinholemay increase in size. As the pinhole becomes larger, electrochemicalreactions may not be able to be sustained due to a lack of reactants inone or more fuel cells 20 and/or in the fuel cell stack 12. This maydecrease the overall fuel cell system 10 efficiency, result in fuel cell20 or fuel cell stack 12 instability, and the inability of the fuel cellsystem 10 to produce power.

Therefore, gas crossover and/or crossover leakage are a key factor thatdetermines the lifetime of a fuel cell stack 12. Leak detection istypically done via a pressure discharge method or by implementingmethods to determine crossover by utilizing hydrogen sensors at theexhaust of a fuel cell system 10. However, hydrogen sensors may notfunction adequately in a humidified environment of the exhaust of thefuel cell system 10, as condensing water often damages such sensors.Additionally, the hydrogen sensor stream may need to be dried, thusadding to the complexity and cost of detecting hydrogen leaks.Therefore, as described below, other systems and methods are needed tosafely and accurately detect hydrogen leaks in the fuel cell system 10.

FIG. 2 illustrates an embodiment of the fuel cell system 10. The fuelcell system 10 comprises the fuel cell stack 12, a fuel supply source160 (e.g., a hydrogen supply source), a coolant source 162, and anoxidant supply source 164. In other embodiments, the fuel cell system 10may include more than one fuel cell stack 12. Flow of fuel (e.g.,hydrogen) from the hydrogen supply source 160 is controlled by a fuelsupply or shut off valve 150 (e.g., hydrogen supply or shut off valve).

When the hydrogen supply valve 150 is switched on, hydrogen from thehydrogen storage 160 flows through a control valve and/or regulator 120and enters an anode inlet 114 of the fuel cell stack 12 (see FIG. 2 ).Typically, during operation and/or shutdown of the fuel cell system 10,hydrogen is consumed at an anode 104 of the fuel cell stack 12 andoxygen is consumed at a cathode 106 of the fuel cell stack 12. A vacuumis created at the anode 104, and nitrogen crosses over from the cathode106 to the anode 104 during passive electrode blanketing or nitrogenblanketing. During passive electrode blanketing or nitrogen blanketingutilized during the fuel cell stack 12 operation and/or shutdown,reactants are consumed with a passive electrical load.

Though the reactants present at the anode 104 may be a mixture ofreactive and non-reactive species, the passive electrical load consumesonly the reactive species leaving the non-reactive species in the fuelcell stack 12. Hydrogen leaks may affect the vacuum of the negativepressure that is created at the anode 104, and thus may impact electrodeblanketing and the shutdown process of the fuel cell system 10.Additionally, the voltage discharge in the fuel cell system 10 may alsochange during hydrogen leaks.

In some embodiments of the present disclosure, as shown in FIG. 2 , apressure and temperature sensor or transmitter 154 in a hydrogenmanifold 153 measures the pressure and temperature in the hydrogenstream 170 entering the fuel cell stack 12 from the hydrogen supplysource 160. A pressure and temperature sensor or transmitter 156monitors the pressure at the anode inlet 114 during the operation,startup, and/or shutdown of the fuel cell stack 12. A pressure switch152 is mounted on a hydrogen supply line 170. If the control valve orregulator 120 fails, then the pressure switch 152 can disable thehydrogen supply valve 150 and stop the flow of hydrogen to the fuel cellsystem 10.

An anode inlet flow 122 enters the fuel cell stack 12 where a portion ofthe hydrogen in the anode inlet flow 122 is consumed. The unconsumedportion of the anode inlet flow 122 exits the fuel cell stack 12 at ananode outlet 107 as an anode outlet flow 126. Typically, the anode inletflow 122 is a mixture of fresh hydrogen and anode exhaust flow, andrecirculated hydrogen via a secondary flow 116. The anode inlet flow 122comprises hydrogen (H₂) fuel, water, and/or inert gases or nitrogen thatmay have diffused with air from the cathode 106 to the anode 104.

The fuel cell system 10 draws in the secondary flow 116 working againstthe pressure losses through a recirculation loop or an anode gasrecirculation (AGR) loop 224. The secondary flow 116, also referred toas a secondary mass flow, an entrainment flow, or a recirculation flow,depends on a flow pressure across the AGR loop 224 and may be determinedby the operation of a recirculation pump, a blower and/or a valve system130. Exhaust hydrogen 96 exits the anode outlet 107 of the fuel cellstack 12 through purge valves 280, 282.

Conversely, referring back to FIG. 2 , the oxidant (e.g., air, oxygen,and/or humidified air) flows from the oxidant supply source 164 into thecathode 106 of the fuel cell stack 12 as cathode inflow 127 at a cathodeinlet 112. The oxidant passes through an air filter 230, a compressorand/or blower 250 before entering the cathode 106 at the cathode inlet112 and exiting as cathode outlet flow 128. The cathode outlet flow 128exits the fuel cell stack 12 at the cathode outlet 109 and as cathodeexhaust 95 by passing through a backpressure valve and/or cathode valve270.

The cathode valve 270 and the purge valves 280, 282 may be variableposition throttle valves with angle sensors 277. The cathode valve 270may be used as an on/off control valve to protect the cathode 106 in thefuel cell stack 12 when it is not in operation. The cathode valve 270may also be used to provide some back pressure to the fuel cell stack12.

The purge valves 280, 282 may be used periodically to remove water,hydrogen, and any buildup of inert gases from the anode 104 in the fuelcell stack 12. Through an engine control unit (ECU) 293, anelectronically and/or pneumatically actuated hydrogen flow system 295 incommunication with the hydrogen supply or shut off valve 150 and thecontrol valve and/or regulator 120 may control the pressure balancebetween the anode 104 and the cathode 106. The electronically and/orpneumatically actuated hydrogen flow system 295 may ensure themechanical robustness of the fuel cell system 10. Hydrogen recirculationthrough the AGR 224 aids in the humidification of the secondary flow 116from the anode outlet 107 to the anode inlet 114 and results in theproduction of a higher anode stoichiometry for fuel cell system 10stability.

As also shown in FIG. 2 , a discharge resistor 290 is attached acrossthe busbars 292 of fuel cell stack 12. The discharge resistor 290 islocated between positive and negative busbars 292 of the fuel cell stack12. For example, the busbars 292 may be connected to a DC/DC or a DC/ACconverter 284 and/or a battery system 286 to distribute power. Atshutdown, a very small current may flow through the discharge resistor290 as hydrogen and/or oxygen may be electrochemically consumed.

The control valve or regulator 120 may be utilized or implemented tocontrol the flow of fresh hydrogen, also referred to as a primary flow,a primary mass flow, a primary fuel, or a motive flow as the anode inletflows 122 into the anode 104. The control valve 120 may be a mechanicalregulator, a proportional control valve, and/or an injector.

The fuel cell system 10 may includes a hydrogen reservoir 180 to store afixed amount of hydrogen that is used during the operation and/orshutdown of the fuel cell system 10. In some embodiments, the hydrogenreservoir 180 may be or comprise a vessel 180 that is appropriatelysized to store enough hydrogen to electrochemically consume the oxygenremaining in the fuel cell stack 12 when the flow of hydrogen andoxidant is stopped during the operation and/or shutdown process.

The hydrogen reservoir 180 may comprise a predetermined length of hoseor tubing (possibly coiled) for storing enough hydrogen toelectrochemically consume the oxygen remaining in the fuel cell stack 12when the flow of hydrogen and oxidant is stopped during operation and/orthe shutdown process. In some embodiments, when the hydrogen reservoir180 is smaller than required, the amount of hydrogen in the hydrogenreservoir 180 is replenished during the operation and/or shutdownprocess so that enough hydrogen is available to electrochemicallyconsume the remaining oxygen.

The volume of hydrogen in the hydrogen reservoir 180 may be determinedbased on the volume required to sustain a voltage discharge duringshutdown. The hydrogen in the hydrogen reservoir 180 may be replenishedby adding hydrogen from an external source into the hydrogen reservoir180. This replenishing or replenishment of the hydrogen reservoir 180may be performed manually or automatically, electronically, and/or inreal-time by one or more controller(s) 294.

Those skilled in the art would appreciate that the amount of hydrogen(or reactant of interest) remaining in the fuel cell stack 12 aftershutdown may be taken into consideration when sizing the hydrogenreservoir 180. Furthermore, the hydrogen reservoir 180 used foroperation and/or shutdown may be located on or in conjunction with thefuel cell stack 12 or off-board the fuel cell stack 12 and/or elsewhereon the fuel cell system 10.

In other embodiments, the fuel cell system 10 may include one or morefuel cell stacks 12. In some embodiments, there may also be one ormultiple valves, sensors, compressors, filters, regulators, blowers,injectors, ejectors, and/or other devices in series and/or in parallelwith the one or more fuel cell stacks 12.

The anode 104 and/or cathode 106 of the fuel cell stack 12 and othercomponents of the fuel cell system 10 may communicate with the one ormore controller(s) 294 via a physical signal, a virtual signal,controller area network bus (CANBUS), or an electronic signal. In someembodiments, the signal may be any type of communicative or computersignal known in the art such as CANBUS.

Physical or virtual sensing systems or methods may be used to enhancethe operation of the fuel cell system 10. For example, a sensing methodmay be used to determine an entrainment ratio (ER) or excess fuel ratioof the fuel cell stack 12. In some embodiments, the physical or virtualsensing systems or methods may comprise one or more pressure sensors ortransmitters (e.g., 154, 156) used to determine a pressure in the anode104 and/or cathode 106. In other embodiments, one or more temperaturesensors or transmitters (e.g., 154, 156) may be used to determine atemperature in the anode 104 and/or cathode 106. In some otherembodiments, one or more voltage sensors may be utilized and/orimplemented to determine stack voltage. The pressure, temperature,and/or voltage sensors may be monitored and/or controlled by thecontroller 294, individually, in groups, and/or collectively. Thesepressure, temperature, and/or voltage may be located at any position inthe stack 12 or system 10, particularly at the anode stack inlet 114and/or at the cathode stack inlet 112.

Hydrogen leaks can occur at any point along the hydrogen supply line170. Typically, a hydrogen leak may occur between the hydrogen supply orshut off valve 150 and one of the purge valves 280, 282. Hydrogen leaksmay occur near fasteners of any of the devices (e.g., the pressureswitch high 152, the pressure and temperature sensors or transmitters154, 156, or the control valve or regulator 120) mounted on the hydrogensupply line 170. Malfunctioning of one or more purge valves 280, 282 mayalso result in a hydrogen leak.

As described earlier, hydrogen leaks can occur within the fuel cellstack 12 due to a crossover flow of gas (e.g., hydrogen, oxidant) acrossthe MEA 22 of the fuel cell stack 12. Though the MEA 22 in the fuel cellstack 12 is minimally permeable when the fuel cell stack 12 is new,hydrogen leaks can occur due to aging, usage, and/or accumulation ofenvironmental contaminants in the fuel cell stack 12. Hydrogen leaks canalso occur due to leaks in seals 31 located in the bipolar plates 28, 30that separate oxidant flow fields 42, fuel flow fields 44, and/orcoolant flow fields 52. Additionally, hydrogen leaks can occur due tocracks in one or more bipolar plates 28, 30 included in the fuel cellstack 12.

Several additional factors affect and/or cause hydrogen leaks in thefuel cell system 10. For example, when a hydrogen leak is within thefuel cell stack 12 and across the membrane electrode assembly (MEA) 22to create a crossover effect, that hydrogen leak is affected by theinternal operating temperature of the fuel cell stack 12, as well as theinternal humidification within the fuel cell stack 12. Furthermore,other environmental factors, such as temperature (e.g., heat or cold)may also affect hydrogen leaks.

As described in the current disclosure, one or more methods may be usedto detect or identify hydrogen leaks in the fuel cells system 10. Themethods may include using the controller 294 to detect, identify, and/orcommunicate the identification and/or repair mechanisms of the hydrogenleaks. In one embodiment, hydrogen leaks may be detected by monitoring arate of voltage discharge in any of the fuel cell stacks 12 of the fuelcell systems 10. Alternatively or additionally, hydrogen leaks may bedetected by monitoring an anode stack inlet pressure decay rate in anyof the fuel cell stacks 12 of the fuel cell systems 10. Alternatively oradditionally, hydrogen leaks may be detected by monitoring a hydrogenmanifold 153 pressure decay rate in any of the fuel cell stacks 12 ofthe fuel cell systems 10.

In one embodiment, the method of detecting hydrogen leaks in the fuelcell system 10 may include assessing a rate of voltage (e.g., stackvoltage) discharge in the fuel cell stack 12. The method may include thecontroller 294 detecting an open purge valve 280, 282 and an externalleak in the anode 104 (or anywhere else) in the fuel cell stack 12 orfuel cell system 10. The method may include the controller 294 detectinga crossover leakage from anode 104 to cathode 106 across the MEA 22 inthe fuel cell system 10. The method may also include the fuel cell stack12 undergoing a freeze preparation state and/or a shutdown via ashutdown process. The method may further include the controller 294performing a hydrogen leak check or detection.

After completion of fuel cell operation, the fuel cell stack 12 mayenter a discharge state where hydrogen and/or oxygen are used toelectrochemically discharge the voltage on the fuel cell stack 12 via adischarge resistor 290. If the hydrogen reservoir 180 containing ahydrogen volume required for the shutdown process is located off-boardthe fuel cell stack 12, then the method of detecting a hydrogen leakincludes the controller 294 toggling or pulsing the hydrogen supply orshut off valve 150 to provide sufficient hydrogen for the stack voltageto discharge in the fuel cell stack 12.

The method may further include monitoring the discharge voltage, therate of voltage discharge, and/or by correlating the rate of voltagedischarge to a leak check value. This correlation may be accomplished orperformed by utilizing, incorporating, interpreting, and/or analyzingdata or information from one or more look-up tables, maps, experimentsand/or calculations. The leak check value may be determined to be anacceptable leak based on the characteristics of the fuel cell system 10.Hydrogen leaks in one or more of the purge valves 280, 282, an externalleak in the fuel cell stack 12, and/or an anode 104 to cathode 106crossover leak may result in a rate of voltage discharge that isdifferent from an expectant rate of voltage. The expectant rate ofvoltage discharge is the rate of voltage discharge of a fuel cell stack12, which has functioning purge valves 280, 282 and an acceptable leakor leakage.

The method of detecting a leak may further include the controller 294monitoring a voltage discharge time. If the voltage discharge time isless than a predetermined discharge time period, the controller 294 mayoutput an error message indicating that the hydrogen leak check hasfailed. Furthermore, the method may include the controller 294 lockingout the fuel cell stack 12 that failed the hydrogen leak check andprevent future operation or the fuel cell stack 12 or system 10.

The predetermined discharge time period may range form about 1 second toabout 300 seconds including any time period or range of time periodcomprised therein. For example, the predetermined discharge time periodmay range form about 1 second to about 60 seconds, about 60 seconds toabout 100 seconds, about 100 seconds to about 150 seconds, about 150seconds to about 200 seconds, about 200 seconds to about 250 seconds, orabout 250 seconds to about 300 seconds. Hydrogen leak rates can bemapped to different stack voltage discharge rates depending on the fuelcell stack 12 design.

FIG. 3 illustrates a simulation 300 of the fuel cell system 10comprising six (6) fuel cell stacks 12-A1, A2, A3, B1, B2, and B3. Thesingle purge valve 280 or 282 of fuel cell stack B3 was driven open viaa power supply during shutdown in the simulation. The power of the fuelcell system 10 is shown by a curve 302. A hydrogen supply to the fuelcell system 10 shown by a curve 304 remains constant. In this example,it takes about 37 seconds for the voltage of fuel cell stack B3, asshown by a curve 306, to discharge to less than about 5 V when one ofthe purge valves 280 or 282 is open. Conversely, the voltage dischargetimes for fuel cell stacks A1, A,2, A3, B1 and B2 are approximately 3minutes, as shown by a curve 308.

The rate of the hydrogen leak is affected by the number of purge valvesthat are open. In one embodiment, a hydrogen leak of about 25 liter perminute (lpm; reference of 0° C., 101.3 kPa) may occur when one of thepurge valves 280 or 282 is open. In other embodiments, hydrogen leaksmay be larger than 25 lpm when more than one purge valve 280, 282 isopen.

In one embodiment, the method of detecting hydrogen leaks in the fuelcell system 10 may further include assessing a minimum anode stack inletpressure at the anode inlet 114. After the voltage discharge process iscompleted, the method may include the controller 294 monitoring aminimum anode negative pressure achieved in a predetermined time period.The predetermined time period can range from about two minutes to abouttwo hours, including any time or range comprised therein. The hydrogensupply or shut off valve 150 may be closed during this assessment.Additionally, the method may include using the pressure and/ortemperature sensor or transmitter 156 to measure the pressure at theanode inlet 114 after the voltage has discharged.

The amount of anode negative pressure determines the occurrence of anyfuel cell stack 12 crossover hydrogen leaks and/or any external hydrogenleaks. If there is a hydrogen leak, instead of the hydrogen beingelectrochemically consumed via the discharge resistor 290 across thefuel cell stack 12, the hydrogen may be exhausted to the externalenvironment. Additionally, the hydrogen may crossover to the cathode 106and combust with air.

The method of detecting hydrogen leaks may further include the systemcontroller 294 monitoring a minimum anode stack inlet pressure that thefuel cell stack 12 achieves in the predetermined time period. The systemcontroller 294 may identify a baseline level of an acceptable leak forthe fuel cell stack 12 at the beginning of life of the fuel cell stack12. The system controller 294 may track the volume of hydrogen leakchange over time.

Less of a vacuum may be formed at the anode 104 of the fuel cell stacks12 if the hydrogen leak is greater than the baseline level of anacceptable hydrogen leak. Furthermore, in large crossovers of hydrogenbetween the anode 104 and the cathode 106, no vacuum may be formed asair would immediately crossover to negate the vacuum. The systemcontroller 294 may determine when to issue an output including adiagnostic alarm message to a user based on the detected hydrogen leak.

FIG. 4 illustrates a graphical representation 400 of hydrogen leaksdetected based on the minimum anode stack inlet pressure in the fuelcell stack 12. The fuel cell system 10 has a baseline leak of less thanabout 14 cubic centimeter (ccm; reference of 0° C., 101.3 kPa) as shownby curve 402. The leaks from the fuel cell stack 12 are in the range ofabout 14 ccm to about 88 ccm (reference of 0° C., 101.3 kPa) of 95%nitrogen and 5% helium, as shown by curves 404, 406, 408, 410. Theminimum anode stack inlet pressure of the fuel cell stack 12 becomesless negative (e.g., becomes more positive) as the size of the leakincreases. Thus, a hydrogen leak can be identified and/or detected bymonitoring the minimum anode stack inlet pressure of the fuel cell stack12.

In one embodiment, the method of detecting hydrogen leaks may includedetermining, detecting, and/or identifying the presence and/or locationof a hydrogen leak in the anode 104. For example, the hydrogen leak maybe greater than about 200 μm in diameter. This detection may occur bymonitoring a rate of pressure drop in the anode 104 at the end ofoperation of the fuel cell system 10. The anode 104 pressure drop may beabout 0.1 psi or greater than 0.1 psi. The rate of pressure drop may bemeasured by the pressure and/or temperature sensor or transmitter 156.End of operation of the system 10 or stack 12 may be defined afterpassage of an additional time period occurring after the fuel cell stack12 has been discharged to a stack voltage of about 5V.

While the fuel cell stack 12 is discharging and during the additionaltime period (e.g., about 300 seconds), the fuel cell stack 12 may have acontinuous supply or a toggling supply (e.g., pulsing, intermittent, orperiodic) of hydrogen. This continuous or toggling supply of hydrogenfeeds into the fuel cell stack 12. The continuous supply or togglingsupply of hydrogen may be regulated by a control valve and/or regulator120 (e.g., a control valve and/or a control regulator).

Alternatively or additionally, the additional time period after the fuelcell stack 12 has discharged to 5V may range from about 1 second toabout 600 seconds including any specific or range of time comprisedtherein. For example, the additional time period after the fuel cellstack 12 has discharged to 5V may range from about 1 second to about 100seconds, about 100 seconds to about 200 seconds, about 200 seconds toabout 300 seconds, about 300 seconds to about 400 seconds, about 400seconds to about 500 seconds, or about 500 seconds to about 600 seconds,including any specific or range of time comprised therein.

In some embodiments, the additional time period after the fuel cellstack 12 has discharged to 5V may be more than about 600 seconds. Usingdifferent additional time periods after the fuel cell stack 12 hasdischarged to 5V may result in a recalibration of the baseline level foracceptable hydrogen leakage. In some embodiments, the method ofdetecting the hydrogen leak of greater than about 200 μm in diameter inthe anode 104 may be implemented for a time period known as a leak checktime. The leak check time may be implemented after the additional timeperiod described above. The leak check time may range from about 10seconds to about 60 seconds, including any specific time period or rangeof time period comprised therein.

FIG. 5 illustrates a graphical representation 500 of the present methodof detecting a hydrogen leak or hydrogen leak detection in the anode 104based on the decay rate of anode stack inlet pressure. As shown by curve502, the fuel cell system 10 has a baseline leak duly based on the fuelcell stack 12 design. Curve 504 identifies a baseline leakage plus anadditional 50 micrometer of hydrogen leakage in the anode 104. Curve 506identifies a baseline leakage plus an additional 100 micrometer ofhydrogen leakage in the anode 104. Curve 508 identifies a baselineleakage plus an additional 200 micrometer of hydrogen leakage in theanode 104. Curve 510 identifies a baseline leakage plus an additional350 micrometer of hydrogen leakage in the anode 104. Curve 512identifies a baseline leakage plus an additional 700 micrometer leakagein the anode 104.

In one embodiment, the method may include detecting the hydrogen leak ofgreater than about 200 μm in diameter in the anode 104 by monitoring arate of pressure drop in the hydrogen manifold 153 at the end ofoperation of the fuel cell system 10. The hydrogen manifold 153 pressuredrop may range from about 30 psi and/or greater than 30 psi. The rate ofpressure drop may be measured by the pressure and/or temperaturetransmitters 154. End of operation may be defined after the additionaltime period of about 300 seconds after the fuel cell stack 12 has beendischarged to a stack voltage of 5V.

FIG. 6 illustrates a graphical representation 600 of hydrogen leakdetection in the anode 104 based on the decay rate of a hydrogenmanifold pressure. The fuel cell system 10 has a baseline leak based onfuel cell stack 12 design, as shown by curve 602. Curve 604 identifies abaseline leakage with an additional 50 micrometer of hydrogen leakage inthe anode 104. Curve 606 identifies a baseline leakage with anadditional 200 micrometer of hydrogen leakage in the anode 104. Curve608 identifies a baseline leakage with an additional 350 micrometer ofhydrogen leakage in the anode 104. Curve 610 identifies a baselineleakage with an additional 700 micrometer of hydrogen leakage in theanode 104.

The one or more controllers 294 for monitoring and/or controlling thecomponents in the fuel cell system 10 may be implemented, in some cases,in communication with hardware, firmware, software, or any combinationthereof present on or outside the system 10 comprising the fuel cell orfuel cell stack 12. The one or more controllers 294 for monitoringand/or controlling the physical or virtual sensors (e.g., 154, 156) usedin the system 10 may be implemented, in some cases, in communicationwith hardware, firmware, software, or any combination thereof present onor outside the system 10 comprising the fuel cell 20 or fuel cell stack12. Information may be transferred to the one or more controllers usingany one or more communication technology (e.g., wired or wirelesscommunications) and associated protocols (e.g., Ethernet, InfiniBand®,Bluetooth®, WiMAX, 3G, 4G LTE, 5G, etc.) to effect such communication.

The one or more controller 294 may be in a computing device. Thecomputing device may be embodied as any type of computation or computerdevice capable of performing the functions described herein, including,but not limited to, a server (e.g., stand-alone, rack-mounted, blade,etc.), a network appliance (e.g., physical or virtual), ahigh-performance computing device, a web appliance, a distributedcomputing system, a computer, a processor-based system, a multiprocessorsystem, a smartphone, a tablet computer, a laptop computer, a notebookcomputer, and a mobile computing device.

The one or more controller 294 may include one or more of aninput/output (I/O) subsystem, a memory, a processor, a data storagedevice, a communication subsystem, and a display that may be connectedto each other, in communication with each other, and/or configured to beconnected and/or in communication with each other through wired,wireless and/or power line connections and associated protocols (e.g.,Ethernet, InfiniBand®, Bluetooth®, Wi-WiMAX, 3G, 4G LTE, 5G, etc.).

The processors may be embodied as any type of computational processingtool or equipment capable of performing the functions described herein.For example, the processor may be embodied as a single or multi-coreprocessor(s), digital signal processor, microcontroller, or otherprocessor or processing/controlling circuit. The memory may be embodiedas any type of volatile or non-volatile memory or data storage capableof performing the functions described herein.

In operation, the memory may store various data and software used duringoperation of the one or more controller 294 such as operating systems,applications, programs, libraries, and drivers. The memory 206 iscommunicatively coupled to the processor via the I/O subsystem, whichmay be embodied as circuitry and/or components to facilitateinput/output operations with the processor, the memory, and othercomponents of the one or more controller 294.

For example, the I/O subsystem may be embodied as, or otherwise include,memory controller hubs, input/output control hubs, sensor hubs, hostcontrollers, firmware devices, communication links (i.e., point-to-pointlinks, bus links, wires, cables, light guides, printed circuit boardtraces, etc.) and/or other components and subsystems to facilitate theinput/output operations.

In one embodiment, the memory may be directly coupled to the processor,for example via an integrated memory controller hub. Additionally, insome embodiments, the I/O subsystem may form a portion of asystem-on-a-chip and be incorporated, along with the processor, thememory, and/or other components of the one or more controller 294, on asingle integrated circuit chip.

The data storage device may be embodied as any type of device or devicesconfigured for short-term or long-term storage of data such as, forexample, memory devices and circuits, memory cards, hard disk drives,solid-state drives, or other data storage devices. The one or morecontroller 294 also includes the communication subsystem, which may beembodied as any communication circuit, device, or collection thereof,capable of enabling communications between the one or more controller294 and other remote devices over the computer network.

The following described aspects of the present invention arecontemplated and non-limiting:

A first aspect of the present invention relates to a method of detectinga hydrogen leak in a fuel cell system. The method comprises initiating ashutdown process of a fuel cell stack in the fuel cell system by acontroller, measuring a volume of hydrogen in a hydrogen reservoir,replenishing the volume of hydrogen in the reservoir when the volume ofhydrogen cannot sustain a voltage discharge during the shutdown process,discharging voltage in the fuel cell stack of the fuel cell system bythe controller, wherein hydrogen and oxygen in the fuel cell stack areconsumed in an electrochemical reaction, measuring a rate of the voltagedischarge by the controller, and detecting the hydrogen leak based onthe rate of the voltage discharge.

A second aspect of the present invention relates to a fuel cell system.The fuel cell system may comprise a fuel cell stack including an anodeand a cathode, a discharge resistor operable to discharge voltage fromthe fuel cell stack, a system controller operable to, measure a rate ofvoltage discharge, and determine and/or identify a presence of ahydrogen leak in the fuel cell system based on the discharge voltage.

In the first aspect of the present invention, the system may comprisedetecting an open purge valve in the fuel cell system. In the firstaspect of the present invention, the voltage may be discharged by adischarge resistor. In the first aspect of the present invention, thehydrogen leak may occur through an external leak or through an anode tocathode crossover in the fuel cell stack.

In the first aspect of the present invention, the method may comprisedetecting the hydrogen leak based on the rate of the voltage dischargecomprises correlating the rate of voltage discharge to an expectant rateof voltage discharge in the fuel cell stack. In the first aspect of thepresent invention, the method may comprise correlating the rate ofvoltage discharge to the expectant rate of voltage discharge comprisesusing a look-up table, a map, an experimental data, or a calculation.

In the first aspect of the present invention, the method may comprisemonitoring a minimum anode negative pressure achieved in a predeterminedtime period. In the first aspect of the present invention, the methodmay comprise determining that a hydrogen supply valve and one or morepurge valves in the fuel cell system are closed before monitoring theminimum anode negative pressure. In the first aspect of the presentinvention, the method may comprise correlating the minimum anodenegative pressure to an acceptable leak value based on a baseline levelof an acceptable leak for the fuel cell stack at beginning of life ofthe fuel cell stack.

In the first aspect of the present invention, the method may comprisemonitoring a minimum anode negative pressure achieved for an additionalperiod after has the fuel cell stack has been discharged to a stackvoltage of about 5V.

In the second aspect of the present invention, the system controller maybe operable to determine the hydrogen leak based on a measurement of aminimum anode negative pressure achieved in a predetermined time period.In the second aspect of the present invention, the additional timeperiod may range from about 2 minutes to about 2 hours. In the secondaspect of the present invention, the system controller may use a look-uptable, a map, an experimental data, or a calculation to determine thehydrogen leak. In the second aspect of the present invention, the systemcontroller may be operable to identify the presence of the hydrogen leakbased on a rate of pressure drop in the anode or a hydrogen manifold atthe end of operation of the fuel cell system.

In the second aspect of the present invention, the pressure drop isafter an additional time period after the end of operation of the fuelcell system. In the second aspect of the present invention, theadditional time period may be about 1 second to about 300 seconds.

In the second aspect of the present invention, the system controller maybe operable to identify the hydrogen leak of greater than about 200 μmin diameter. In the second aspect of the present invention, thedischarge resistor may be operable to discharge voltage from the fuelcell stack for voltage discharge time, and wherein the controller may beoperable to output an error message indicating that the hydrogen leakcheck has failed if the voltage discharge time is less than apredetermined discharge time period. In the second aspect of the presentinvention, the predetermined discharge time period may be about 1 secondto about 50 seconds.

The features illustrated or described in connection with one exemplaryembodiment may be combined with any other feature or element of anyother embodiment described herein. Such modifications and variations areintended to be included within the scope of the present disclosure.Further, a person skilled in the art will recognize that terms commonlyknown to those skilled in the art may be used interchangeably herein.

The above embodiments are described in sufficient detail to enable thoseskilled in the art to practice what is claimed and it is to beunderstood that logical, mechanical, and electrical changes may be madewithout departing from the spirit and scope of the claims. The detaileddescription is, therefore, not to be taken in a limiting sense.

As used herein, an element or step recited in the singular and proceededwith the word “a” or “an” should be understood as not excluding pluralof said elements or steps, unless such exclusion is explicitly stated.Furthermore, references to “one embodiment” of the presently describedsubject matter are not intended to be interpreted as excluding theexistence of additional embodiments that also incorporate the recitedfeatures. Specified numerical ranges of units, measurements, and/orvalues comprise, consist essentially or, or consist of all the numericalvalues, units, measurements, and/or ranges including or within thoseranges and/or endpoints, whether those numerical values, units,measurements, and/or ranges are explicitly specified in the presentdisclosure or not.

Unless defined otherwise, technical and scientific terms used hereinhave the same meaning as is commonly understood by one of ordinary skillin the art to which this disclosure belongs. The terms “first,”“second,” “third” and the like, as used herein do not denote any orderor importance, but rather are used to distinguish one element fromanother. The term “or” is meant to be inclusive and mean either or allof the listed items. In addition, the terms “connected” and “coupled”are not restricted to physical or mechanical connections or couplings,and can include electrical connections or couplings, whether direct orindirect.

Moreover, unless explicitly stated to the contrary, embodiments“comprising,” “including,” or “having” an element or a plurality ofelements having a particular property may include additional suchelements not having that property. The term “comprising” or “comprises”refers to a composition, compound, formulation, or method that isinclusive and does not exclude additional elements, components, and/ormethod steps. The term “comprising” also refers to a composition,compound, formulation, or method embodiment of the present disclosurethat is inclusive and does not exclude additional elements, components,or method steps.

The phrase “consisting of” or “consists of” refers to a compound,composition, formulation, or method that excludes the presence of anyadditional elements, components, or method steps. The term “consistingof” also refers to a compound, composition, formulation, or method ofthe present disclosure that excludes the presence of any additionalelements, components, or method steps.

The phrase “consisting essentially of” or “consists essentially of”refers to a composition, compound, formulation, or method that isinclusive of additional elements, components, or method steps that donot materially affect the characteristic(s) of the composition,compound, formulation, or method. The phrase “consisting essentially of”also refers to a composition, compound, formulation, or method of thepresent disclosure that is inclusive of additional elements, components,or method steps that do not materially affect the characteristic(s) ofthe composition, compound, formulation, or method steps.

Approximating language, as used herein throughout the specification andclaims, may be applied to modify any quantitative representation thatcould permissibly vary without resulting in a change in the basicfunction to which it is related. Accordingly, a value modified by a termor terms, such as “about,” and “substantially” is not to be limited tothe precise value specified. In some instances, the approximatinglanguage may correspond to the precision of an instrument for measuringthe value. Here and throughout the specification and claims, rangelimitations may be combined and/or interchanged. Such ranges areidentified and include all the sub-ranges contained therein unlesscontext or language indicates otherwise.

As used herein, the terms “may” and “may be” indicate a possibility ofan occurrence within a set of circumstances; a possession of a specifiedproperty, characteristic or function; and/or qualify another verb byexpressing one or more of an ability, capability, or possibilityassociated with the qualified verb. Accordingly, usage of “may” and “maybe” indicates that a modified term is apparently appropriate, capable,or suitable for an indicated capacity, function, or usage, while takinginto account that in some circumstances, the modified term may sometimesnot be appropriate, capable, or suitable.

It is to be understood that the above description is intended to beillustrative, and not restrictive. For example, the above-describedembodiments (and/or aspects thereof) may be used individually, together,or in combination with each other. In addition, many modifications maybe made to adapt a particular situation or material to the teachings ofthe subject matter set forth herein without departing from its scope.While the dimensions and types of materials described herein areintended to define the parameters of the disclosed subject matter, theyare by no means limiting and are exemplary embodiments. Many otherembodiments will be apparent to those of skill in the art upon reviewingthe above description. The scope of the subject matter described hereinshould, therefore, be determined with reference to the appended claims,along with the full scope of equivalents to which such claims areentitled.

This written description uses examples to disclose several embodimentsof the subject matter set forth herein, including the best mode, andalso to enable a person of ordinary skill in the art to practice theembodiments of disclosed subject matter, including making and using thedevices or systems and performing the methods. The patentable scope ofthe subject matter described herein is defined by the claims, and mayinclude other examples that occur to those of ordinary skill in the art.Such other examples are intended to be within the scope of the claims ifthey have structural elements that do not differ from the literallanguage of the claims, or if they include equivalent structuralelements with insubstantial differences from the literal languages ofthe claims.

While only certain features of the invention have been illustrated anddescribed herein, many modifications and changes will occur to thoseskilled in the art. It is, therefore, to be understood that the appendedclaims are intended to cover all such modifications and changes as fallwithin the true spirit of the invention.

What is claimed is:
 1. A method of detecting a hydrogen leak in a fuelcell system comprising: initiating a shutdown process of a fuel cellstack in the fuel cell system by a controller, measuring a volume ofhydrogen in a hydrogen reservoir, replenishing the volume of hydrogen inthe reservoir when the volume of hydrogen cannot sustain a voltagedischarge during the shutdown process, discharging voltage in the fuelcell stack of the fuel cell system by the controller, wherein hydrogenand oxygen in the fuel cell stack are consumed in an electrochemicalreaction, measuring a rate of the voltage discharge by the controller,and detecting the hydrogen leak based on the rate of the voltagedischarge.
 2. The method of claim 1, wherein the voltage is dischargedby a discharge resistor.
 3. The method of claim 1, further comprisingdetecting an open purge valve in the fuel cell system.
 4. The method ofclaim 1, wherein the hydrogen leak occurs through an external leak orthrough an anode to cathode crossover in the fuel cell stack.
 5. Themethod of claim 1, wherein detecting the hydrogen leak based on the rateof the voltage discharge comprises correlating the rate of voltagedischarge to an expectant rate of voltage discharge in the fuel cellstack.
 6. The method of claim 5, wherein correlating the rate of voltagedischarge to the expectant rate of voltage discharge comprises utilizinga look-up table, a map, an experimental data, or a calculation.
 7. Themethod of claim 1, comprising monitoring a minimum anode negativepressure achieved in a predetermined time period.
 8. The method of claim7, further comprising determining that a hydrogen supply valve and oneor more purge valves in the fuel cell system are closed beforemonitoring the minimum anode negative pressure.
 9. The method of claim7, comprising correlating the minimum anode negative pressure to anacceptable leak value based on a baseline level of an acceptable leakfor the fuel cell stack at beginning of life of the fuel cell stack. 10.The method of claim 1, comprising monitoring a minimum anode negativepressure achieved for an additional time period after the fuel cellstack has been discharged to a stack voltage of about 5V.
 11. The methodof claim 10, wherein the additional time period ranges from about 2minutes to about 2 hours.
 12. A fuel cell system comprising: a fuel cellstack including an anode and a cathode, a discharge resistor operable todischarge voltage from the fuel cell stack, a system controller operableto measure a rate of voltage discharge and identify a presence of ahydrogen leak in the fuel cell system based on the discharge voltage.13. The fuel cell system of claim 12, wherein the system controller isoperable to determine the hydrogen leak based on a measurement of aminimum anode negative pressure achieved in a predetermined time period.14. The fuel cell system of claim 12, wherein the system controllercomprises a look-up table, a map, an experimental data, or a calculationto identify the location or presence of the hydrogen leak.
 15. The fuelcell system of claim 12, wherein the system controller is operable toidentify the presence of the hydrogen leak based on a rate of pressuredrop in the anode or a hydrogen manifold of the fuel cell system. 16.The fuel cell system of claim 15, wherein the pressure drop is after anadditional time period at the end of operation of the fuel cell system.17. The fuel cell system of claim 16, wherein the additional time periodranges from about 1 second to about 300 seconds.
 18. The fuel cellsystem of claim 12, wherein the system controller is operable toidentify the presence of the hydrogen leak that is greater than about200 μm in diameter.
 19. The fuel cell system of claim 12, wherein thedischarge resistor is operable to discharge the voltage from the fuelcell stack for a voltage discharge time, and wherein the systemcontroller is operable to output an error message when the voltagedischarge time is less than a predetermined discharge time period. 20.The fuel cell system of claim 19, wherein the predetermined dischargetime period ranges from about 1 second to about 50 seconds.